The present invention relates generally to the art of welding.
It has heretofore been generally known to utilize back-up tapes of either a relatively thick ceramic material or a flexible fiberglass tape material for the making of one-side welds and root pass back-up of two-side welds in connection with inert gas welding (TIG or MIG). In the known arrangements, provision is usually made for securing the back-up tape in bridging relation over the adjacently spaced edges of the workpieces that are to be welded along a seam line.
In some of the known embodiments, the back-up fiberglass tape or ceramic sections are secured to an aluminum foil backing which has marginal lateral edge portions that extend beyond the respective adjacent edges of the back-up material and are coated with a pressure sensitive adhesive covered with a removable liner. A roller or other means is generally used in this type of arrangement to obtain a good adhesion of the foil edges to the surface of the associated workpieces.
In another known embodiment, a granular back-up flux is molded and mounted on a flexible adhesive tape.
In use, it has been found that the use of an adhesive entails certain time consuming preparation of the workpiece surfaces in order to assure that such surfaces are properly cleaned. If the tape adhesive engages with a dirty surface, it will not effectively adhere to the workpiece, and the back-up strip will not be held in a proper position in relation to the welding seam. For this reason, it will be appreciated that although the ceramic or fiberglass back-up tape, as described above, might not be damaged in the welding operation and might be in itself reusable, the contamination of the adhesive surface of the foil would prevent reuse of the mounting foil with the back-up tape as a composite assembly. Thus, the known arrangement as just described entails a rather costly procedure, particularly in those cases in which a large number of welds are to be made as a part of a production schedule.
Attempts have therefore been made to provide an arrangement which would overcome the disadvantages of the above mentioned procedure, and for such purpose it has heretofore been proposed to utilize a rather cumbersome and complicated clamping bracket which could be magnetically attached to the surfaces of the workpieces to be welded. In one known bracket structure, the bracket includes an adjustable screw means which is carried by the bracket and is manually operable to mechanically forcibly hold one or more channel shaped holders in an operative position over the weld line, each holder being adapted to hold a plurality of ceramic back-up sections in pressure engagement over the adjacent edges of the workpiece along the seam line. While these clamping brackets and holders are reusable, and in this respect are an improvement over the use of an adhesive foil backing, the complexity and construction of the clamping brackets makes them relatively more expensive.
Tests conducted by applicant have indicated that the known concepts and devices do not embody all that could be desired for the most efficacious production of one-side welds. For example, in order to most efficiently utilize the less expensive fiberglass tapes, it is an important consideration that the tape back-up means should embody an effective heat sink means for conducting heat away from the tape during the welding operation, in order to limit and control the extent of tape melting and the formation of a smooth and uniform back surface of the deposited weld material. The presently used foil mounted tapes and channel shaped holders for the ceramic sections do not have the requisite high heat conducting characteristics to form a sufficiently effective heat sink to permit the use of the less expensive flexible fiberglass tapes.
Briefly, according to the present invention, it is proposed to utilize channel shaped holders which are designed to receive the flexible fiberglass tape lengthwise therein, and in which bars of a high heat conducting material such as copper or aluminum are interposed between the tape and the channel holder in underlying relation to the tape. Also, instead of the complicated magnetically attachable brackets with their pressure applying screws, it is proposed to provide in the present invention a simplified holding bracket in which a bowed spring mounts a magnet at each end. By placing the spring in tranversely extending position of engagement with a channel shaped holder, the spring will be flexed by movement of its end magnets into engagement with adjacent surfaces of the associated work pieces in such a manner as to forcibly apply a holding pressure against the channel holders and the associated fiberglass tape.